Net Income per Common Share - Reconciliation between basic and diluted net income per share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Apr. 30, 2019	Apr. 30, 2018
Net Income per Common Share
Net income (in dollars)	$ 12,043	$ 9,885
Basic net income per share:
Basic common shares	48,781	49,127
Basic net income per share (in dollars per share)	$ 0.25	$ 0.20
Diluted net income per share:
Basic common shares	48,781	49,127
Diluted restricted stock awards and stock options	993	1,010
Diluted common shares	49,774	50,137
Diluted net income per share (in dollars per share)	$ 0.24	$ 0.20